This application is based on and claims priority to Japanese Patent Application No. 10-328376, filed Nov. 18, 1998, the entire contents of which is hereby expressly incorporated by reference.
1. Field of the Invention
This invention relates to an outboard drive and more particularly to a system for cooling a driveshaft housing for an outboard drive.
2. Description of the Related Art
Outboard motors are popular for use in powering watercraft. Such outboard motors typically are affixed to a transom of the watercraft and include a power head, which encloses an engine within a protective cowling. A driveshaft housing depends from the power head and encloses a driveshaft. A lower unit depends from the driveshaft housing and encloses a transmission, which transmits power from the driveshaft to a propeller shaft. A propeller rotates with the propeller shaft, thus propelling the watercraft.
An exhaust system for the engine typically includes an exhaust passage that extends from the engine through the driveshaft housing into the lower unit and terminates at a discharge port in the lower unit. The exhaust system may include various structures including mufflers, expansion chambers and catalysts. In most exhaust passage designs, the exhaust passage is sufficiently close to the driveshaft housing that the heat of the exhaust gases is at least partially transmitted to the driveshaft housing.
Typical outboard motors have no system for cooling the driveshaft housing. Instead, the driveshaft housing is simply exposed to the surrounding atmosphere and relies upon air convection for cooling. Conversely, the lower unit, which depends from the driveshaft housing, is at least partially submerged in water during normal use of the watercraft. Thus, heat transferred from the exhaust gases to the lower unit housing is transferred from the housing to the surrounding water, thus cooling the lower unit.
The driveshaft housing may be heated to high temperatures by the exhaust gases under some operating conditions. As such, the driveshaft housing may sustain heat damage. For example, the external side of the heated driveshaft housing may become discolored by the heat, marring the appearance of the outboard motor.
Accordingly, a need exists for an outboard drive having a cooling system adapted to dissipate heat transferred to the driveshaft housing from exhaust gases within the exhaust system.
In accordance with one aspect, the present invention provides an outboard motor comprising a power head having an engine and a surrounding protective cowling. A driveshaft housing depends from the power head and at least partially encloses a driveshaft depending from the engine. The driveshaft housing has an outer surface. A lower unit depends from the driveshaft housing and at least partially encloses a transmission, which communicates with the driveshaft. The lower unit also includes a propulsion device. An exhaust system is provided for discharging exhaust gases from the engine. The exhaust system includes an exhaust passage which extends at least partially through the driveshaft housing. A cooling system includes a pump, a delivery conduit communicating with the pump, and at least one outlet. The outlet is arranged so as to deliver coolant from the delivery conduit to at least a portion of the outer surface of the driveshaft housing.
The driveshaft housing can also include an outwardly-extending step formed on the outer surface of the housing. An outer shroud can depend from the protective cowling to a pont adjacent to the step, such that a gap is formed between the step and the outer shroud. The outlet of the cooling system can be positioned between the shroud and the driveshaft housing.
Another aspect of the present invention involves an outboard motor comprising a power head having an engine and a surrounding protective cowling. A driveshaft housing depends from the power head and at least partially encloses a driveshaft depending from the engine. The driveshaft housing includes an outer casing. A lower unit depends from the driveshaft housing and at least partially encloses a transmission which communicates with the driveshaft. The lower unit also includes a propulsion device. An exhaust system discharges exhaust gases from the engine and includes an exhaust guide which extends at least partially through the driveshaft housing. Cooling means is provided for reducing the temperature of at least a portion of the outer casing of the driveshaft housing.
An additional aspect of the present invention involves an outboard drive comprising a housing at least partially enclosing a driveshaft and including an outer surface. A lower unit depends from the housing and at least partially encloses a transmission communicating with the driveshaft. The lower unit includes a propulsion device. An exhaust system is provided and includes an exhaust passage extending at least partially through the housing. A cooling system is also provided and includes a pump, a delivery conduit communicating with the pump, and at least one outlet arranged to deliver coolant from the delivery conduit to at least a portion of the outer surface of the housing.
For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment(s) disclosed.